It is proposed to characterize the state of polyoma viral DNA in polyoma transformed cells and in tumors induced in hamsters by polyoma virus. Viral DNA in the appropriate cells will be extracted and digested with bacterial restriction enzymes and the characteristic fragments detected by gel electrophoresis and specific hybridization to radioactive polyoma c-RNA. These specific fragments will be compared to those produced from vegetative DNA to detect the sites of recombination with cellular DNA. The structure and biology of human hepatitis B virus DNA is being investigated in a similar manner in order to learn whether this virus is involved in certain hepatomas. BIBLIOGRAPHIC REFERENCES: Summers, Jesse. A physical map of polyoma viral DNA fragments produced by cleavage with a restriction enzyme from Hemophilus aegyptius, endonuclease R. Hae III. J. Virol. 15: 946-953, 1975. Summers, Jesse, Anna O'Connell and Irving Millman. The genome of Hepatitis B virus: restriction enzyme cleavage and structure of the DNA extracted from Dane particles. Proc. Natl. Acad. Sci., U.S.A. 72: 4597-4601, 1975.